Since 9/11, the U.S. has spent more than $1.1 trillion on homeland security.

To a large number of security analysts, this expenditure makes no sense. The vast cost is not worth the infinitesimal benefit. Not only has the actual threat from terror been exaggerated, they say, but the great bulk of the post-9/11 measures to contain it are little more than what Schneier mocks as “security theater”: actions that accomplish nothing but are designed to make the government look like it is on the job. In fact, the continuing expenditure on security may actually have made the United States less safe.

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Two months after 9/11, the Bush administration created the Transportation Security Agency, ordering it to hire and train enough security officers to staff the nation’s 450 airports within a year. Six months after that, the government vastly expanded the federal sky-marshal program, sending thousands of armed lawmen to ride planes undercover. Meanwhile, the T.S.A. steadily ratcheted up the existing baggage-screening program, banning cigarette lighters from carry-on bags, then all liquids (even, briefly, breast milk from some nursing mothers). Signs were put up in airports warning passengers about specifically prohibited items: snow globes, printer cartridges. A color-coded alert system was devised; the nation was placed on “orange alert” for five consecutive years. Washington assembled a list of potential terror targets that soon swelled to 80,000 places, including local libraries and miniature-golf courses. Accompanying the target list was a watch list of potential suspects that had grown to 1.1 million names by 2008, the most recent date for which figures are available. Last year, the Department of Homeland Security, which absorbed the T.S.A. in 2003, began deploying full-body scanners, which peer through clothing to produce nearly nude images of air passengers.

Bruce Schneier’s exasperation is informed by his job-related need to spend a lot of time in Airportland. He has 10 million frequent-flier miles and takes about 170 flights a year; his average speed, he has calculated, is 32 miles and hour. “The only useful airport security measures since 9/11,” he says, “were locking and reinforcing the cockpit doors, so terrorists can’t break in, positive baggage matching”—ensuring that people can’t put luggage on planes, and then not board them —“and teaching the passengers to fight back. The rest is security theater.”

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Terrorists will try to hit the United States again, Schneier says. One has to assume this. Terrorists can so easily switch from target to target and weapon to weapon that focusing on preventing any one type of attack is foolish. Even if the T.S.A. were somehow to make airports impregnable, this would simply divert terrorists to other, less heavily defended targets—shopping malls, movie theaters, churches, stadiums, museums. The terrorist’s goal isn’t to attack an airplane specifically; it’s to sow terror generally. “You spend billions of dollars on the airports and force the terrorists to spend an extra $30 on gas to drive to a hotel or casino and attack it,” Schneier says. “Congratulations!”

What the government should be doing is focusing on the terrorists when they are planning their plots. “That’s how the British caught the liquid bombers,” Schneier says. “They never got anywhere near the plane. That’s what you want—not catching them at the last minute as they try to board the flight.”

To walk through an airport with Bruce Schneier is to see how much change a trillion dollars can wreak. So much inconvenience for so little benefit at such a staggering cost. And directed against a threat that, by any objective standard, is quite modest. Since 9/11, Islamic terrorists have killed just 17 people on American soil, all but four of them victims of an army major turned fanatic who shot fellow soldiers in a rampage at Fort Hood. (The other four were killed by lone-wolf assassins.) During that same period, 200 times as many Americans drowned in their bathtubs. Still more were killed by driving their cars into deer. The best memorial to the victims of 9/11, in Schneier’s view, would be to forget most of the “lessons” of 9/11. “It’s infuriating,” he said, waving my fraudulent boarding pass to indicate the mass of waiting passengers, the humming X-ray machines, the piles of unloaded computers and cell phones on the conveyor belts, the uniformed T.S.A. officers instructing people to remove their shoes and take loose change from their pockets. “We’re spending billions upon billions of dollars doing this—and it is almost entirely pointless. Not only is it not done right, but even if it was done right it would be the wrong thing to do.”